The organization of the brain vasomotor center and its interrelations with diencephalic and forebrain stations of the vasomotor system will be studied. Only with detailed information about the organization of the vasomotor system will it be possible to understand how its final motor output, sympathetic discharge, arises from the interactions of individual neurons. Two major approaches will be used: (a) Analysis of the functional connections of the different stations of the vasomotor system by combinations of stimulation, recordings, and lesions, and (b) Identification of vasomotor neurons through analysis of temporal relations of unit activity to peripheral sympathetic discharge. Experiments will be performed on decerebrate or urethane- anesthetized cats with neuromuscular blockade, vagotomy, and artificial ventilation. The major method of analysis will involve electrical stimulation (single shocks, short trains at high frequency, repetitive stimulation) of brain stem and forebrain regions combined with electrical recording from whole splanchnic nerve and from brain stem and spinal cord region via macroelectrodes or microelectrodes. Digital logic programs will be used to derive patterns and sequences of stimulation. Special attention will be paid to latency relationships. The data will be analyzed by computation of averaged (summed) responses to reveal temporal relationships; the method of auto and cross correlation functions will also be used, where appropriate. Information will be obtained which will be relevant to the understanding of the alterations leading to various pathological conditions, e.g., hypertension, as well as the responses to various stresses, e.g., shock.